1. Field of the invention
This invention relates to an electrophotographic device, particularly to an electrophotographic device to be used in contact charging process.
2. Related Background Art
The main stream of the charging process in the electrophotographic system is by way of corona discharging, but in this system, there are involved such problems as denaturation of the photosensitive member on account of corona products such as ozone, NOx, etc. during corona generation, influence of the discharging wire on image quality, formation of white drop-outs on black streaks on image, etc. Also, there is the drawback that efficiency is poor in power energy.
For compensation of such drawbacks, there have been studied in the prior art the method of direct charging, and a large number of proposals have been made (Japanese Laid-open Patent Application Nos. 57-178267, 56-104351, 58-40566, 58-139156, 58-150975, etc.). This method is to charge the photosensitive member surface by applying a voltage with the member for charging in contact with the electrophotographic photosensitive member. As the shape of the member for charging, such shape as roller, brush (including magnetic brush), plate blade, belt, etc. can be taken, but in view of miniaturization of the electrophotographic device, a plate blade shape is preferred among them. This is because, a nip width enough to obtain better charging characteristic with small space can be taken as compared with other shapes.
However, when charging is effected by use of a blade for charging, through the friction between the photosensitive member surface and the blade contacting portion, reversal of the blade (turnover) or the chatter phenomenon occurs, whereby there is the problem that no good image can be obtained. In the case of a cleaning blade to be used in the cleaning process, the frictional force between the photosensitive member and the blade can be alleviated due to the presence of a toner or a lubricant therebetween, but since nothing exists between the photosensitive member and the blade in the direct charging process, it is more disadvantageous for blade reversal and the chatter phenomenon.